Chlorine-containing polymers such as a vinyl chloride polymer are liable to be colored by heat-decomposition reaction such as de-hydrochlorination or to be reduced in mechanical properties in heat molding processing or subsequent heat histories. To prevent the above troubles, it is generally required to compound stabilizers.
Olefin-type resins produced by using Ziegler-type catalysts contain halogen-containing catalyst residues. These residues generate hydrogen chloride at the time of heating and molding to cause rust in the molding machines or generate deterioration in the resins, for example, yellowing. To prevent this deterioration, stabilizers which trap hydrogen chloride were compounded widely.
The use of hydrotalcite as such a stabilizer has been knonwn from old. For example, Japanese Laid-Open Patent Publication No. 80445/1980 describes that hydrotalcite is used as a stabilizer for halogen-containing resins. Further, Japanese Patent Publication No. 36012/1983 shows that a .beta.-diketone compound and a hydrotalcite of formula (1) EQU Mg.sub.1-x.Al.sub.x (OH).sub.2.A.sub.x/2.mH.sub.2 O (1)
wherein x denotes a number of 0&lt;.ltoreq.&lt;0.5, A represents CO.sub.3.sup.2- or SO.sub.4.sup.2-, and m represents a positive number are compounded in a halogen-containing resin. PA1 wherein M represents Mg, Ca or Zn, A represents CO.sub.3 or HPO.sub.4, x, y and z represent a positive number, and a is zero or a positive number, PA1 wherein m is 0 or a positive number. PA1 wherein X is an inorganic or organic anion, n is the valence of the anion, and m is a number of 3 or below, PA1 wherein I(002) represents a relative intensity of an X-ray diffraction PA1 wherein X represents an inorganic anion composed mainly of a carbonic acid radical, M represents an alkali metal composed mainly of lithium, m is a number of 1.5 to 2.5, n is a number of 0.1 to 1, and k is a number of 0 to 10, PA1 the lamination asymmetry index (Is) being EQU defined by Is=tan .theta..sub.2 /tan .theta..sub.1 (7) PA1 (wherein .theta..sub.1 represents an angle formed between a peak perpendicular and a peak tangent on the narrow angle side at an X-ray diffraction peak of a fixed spacing, and .theta..sub.2 represents an angle formed between the peak perpendicular and a peak tangent on the wide angle side at the peak), PA1 wherein X represents an inorganic anion composed mainly of a carbonic acid radical, M represents an alkali metal composed mainly of sodium, m represents a number of 0.5 to 1.5, n represents a number of 0.1 to 1 and k represents a number of 0 to 3,
Furthermore, Japanese Patent Publication No. 30737/1984 discloses that at least 0.01% by weight of a complex compound represented by general formula (2) EQU M.sub.x Al.sub.y (OH).sub.2x+3y-2z (A).sub.z.aH.sub.2 O (2)
is compounded in a polyolefin containing halogen-containing catalyst residues produced by using a Ziegler-type catalyst.
Hydrotalcites are non-toxic complex hydroxide and carbonate salts of magnesium and aluminum, have excellent heat stability, and are transparent when compounded in a polymer.
These hydrotalcites ideally have a chemical composition expressed by formula (3) EQU Mg.sub.6 Al.sub.2 (OH).sub.16.CO.sub.3.mH.sub.2 O (3)
However, Mg and Al, within a very broad range, form a solid solution as shown by formula (1) or (2), and there is a problem in that it is difficult to form a composition having a strictly constant composition.
A report of C. J. Serna et al. entitled "Crystal-Chemical Study of Layered [Al.sub.2 Li(OH).sub.6 ].sup.+ X.sup.-.nH.sub.2 O" (Clays and Clay Minerals, Vol. 25, page 384 (1977)) describes that a lithium aluminum complex hydroxide salt is synthesized by adding a benzene solution of aluminum tri(sec-butoxide) (ASB) as liquid drops to an excessive aqueous solution of lithium carbonate, hydrolyzing ASB, washing the resulting gel, and thereafter, hydrothermally treating the washed gel for several days at 130.degree. C.
A report of I. Sissoko et al. entitled "Anion Intercalation and Exchange in Al(OH).sub.3 -Derived Compounds" (Journal of Solid State Chemistry, Vol. 25, pages 283-288 (1985) describes that a lithium aluminum complex hydroxide salt is produced by adding AlCl.sub.3 as liquid drops to an aqueous solution containing LiOH and Na.sub.2 CO.sub.3 (or Na.sub.2 SO.sub.4), changing the pH from 13 in the early period to 10.2 in the last stage to form a gel-like precipitate, and aging the precipitate with stirring (see Comparative Example 6 and FIG. 6 to be given below).
U.S. Pat. Nos. 4,116,856 and 4,221,767 disclose that crystals of lithium. aluminum complex hydroxide salt are produced by reacting amorphous Al(OH).sub.3 or crystalline hydrated alumina (such as nordstrandite, bayerite, gibbsite) with LiOH, and then reacting the mixture with LiX (wherein X represents a halide). However, the resulting crystals are sol-like and are very difficult to filter.
U.S. Pat. Nos. 5,356,567, 5,360,859, and 5,419,883 describe a lithium aluminum complex hydroxide salt (to be referred to as LAHS) of general formula (4) EQU [Al.sub.2 Li(OH).sub.6 ].sub.n X.mH.sub.2 O (4)
having at least 10, especially at least 20 of an orientation degree (OD) defined by formula (5) EQU OD=I(002)/I(110) (5)
(Cu-K.alpha.) peak appearing in the index of a plane (002) at a spacing (d) of 7.67 to 7.84 .ANG., and I(110) represents a relative intensity of an X-ray diffraction (Cu-K.alpha.) peak appearing in the index of a plane (110) at a spacing (d) of 4.41 to 4.45 .ANG..
For example, as typical examples of LAHS, lithium carbonate and aluminum chloride are reacted in an aqueous solution in the presence of sodium carbonate and sodium hydroxide, a higher fatty acid or a surface-active agent is added as an orientation enhancer to the reaction mixture, and the mixture is treated at a temperature of 60 to 100.degree. C. so that the degree of orientation becomes at least 10.
As another type of the alkali aluminum complex hydroxide carbonate salt, sodium aluminum complex hydroxide carbonate salts having a dawsonite-type crystal structure are known. Methods of synthesizing these salts are known from Japanese Patent Publication No. 38318/1972, Japanese Patent Publication No. 17718/1979, Japanese Laid-Open Patent Publication No. 22628/1981, Japanese Patent Publication No. 44604/1982, Japanese Laid-Open Patent Publication No. 61625/1982, Japanese Laid-Open Patent Publication No. 83933/1984, Japanese Laid-Open Patent Publication No. 100017/1988, Japanese Patent Publication No. 24731/1989, Japanese Patent Publication No. 58205/1990 and Japanese Laid-Open Patent Publication No. 271116/1991.
As a synthesizing method of the above product, Japanese Patent Publication 38313/1972 discloses a method of producing dawsonite which comprises reacting an aluminum salt and sodium carbonate using at least 2 moles of CO.sub.2 per mole of Al.sub.2 O.sub.3, and maintaining the pH of the reaction mixture at 7.2 to 10.5.
However, LAHS synthesized by these known methods is in the form of gel-like particles, and the growth of crystals is still insufficient. The shape and size of these particles are non-uniform, and are still unsatisfactory as a compounding agent for resins.
Furthermore, dawsonite is fibrous. Many of these fibers are entangled in the form of fibrous ball. Accordingly, they are still unsatisfactory in use as a compounding agent for resins.
Furthermore, synthesizing methods for known alkali aluminum complex hydroxide carbonate salts must treat the starting materials and the products as a dilute solution or slurry. Otherwise, the liquids have a high viscosity, and their stirring is difficult. Thus, the productivity is low, and the cost of production is high. Another problem is that the resulting alkali aluminum complex hydroxide carbonate salts are very difficult to filter, and a long period of time is required for the filtration process.
The fate of the alkali aluminum complex hydroxide carbonate salts is that it is essential to use alkali metal compounds as a starting material. These resulting products contain free alkali metal components as impurities in addition to alkali metal components charged into the compounds. These free alkali metal components lead to the defect that they may color the resins in which these alkali metal components are compounded.